Solar and wind energy provide renewable, non-polluting energy sources, as opposed to conventional non-renewable, polluting energy sources, such as coal or oil. Because of this, solar and wind energy have become increasingly important as energy sources that may be converted into electricity. For solar energy, photovoltaic panels arranged in an array typically provide the means to convert solar energy into electrical energy. Similar arrays may be implemented for harvesting energy from wind or other natural energy sources.
In operating a photovoltaic array, maximum power point tracking (MPPT) is generally used to automatically determine a voltage or current at which the array should operate to generate a maximum power output for a particular temperature and solar irradiance. Although MPPT for the entire array is relatively easy to perform when the array is operating under ideal conditions (i.e., the same irradiance, temperature and electrical features for each panel in the array), when there are mismatches or partially shaded conditions, MPPT for the array as a whole is more complicated. In this situation, MPPT techniques may not provide accurate results due to relative optima of the multi-peak power-to-voltage characteristics of the mismatched array. As a result, only a few of the panels in the array may be operating ideally. This causes a drastic drop in power production because, for an array that includes strings of panels, the least efficient panel in a string determines the current and efficiency for the entire string.
Because of this, some photovoltaic systems provide a DC-DC converter for each panel in the array. Each of these DC-DC converters performs MPPT to find a maximum power point for its corresponding panel. However, solar energy is wasted when the DC-DC converters are not powered up before irradiance reaches a level high enough to generate electricity. Keeping the converters always powered up would solve this problem. However, this would also result in the additional problem of wasting energy used for powering up the converters. As the converters do not need to operate when the irradiance is at a relatively low level, using energy for powering up the converters at these times would be inefficient.